Gutsche I, Holzinger J, Rauh N, Baumeister W, May R P
Max-Planck-Institute for Biochemistry, Am Klopferspitz 18a, Martinsried bei München, D-82152, Germany.
J Struct Biol. 2001 Aug;135(2):139-46. doi: 10.1006/jsbi.2001.4373.
Protein folding by chaperonins is powered by ATP binding and hydrolysis. ATPase activity drives the folding machine through a series of conformational rearrangements, extensively described for the group I chaperonin GroEL from Escherichia coli but still poorly understood for the group II chaperonins. The latter--archaeal thermosome and eukaryotic TRiC/CCT--function independently of a GroES-like cochaperonin and are proposed to rely on protrusions of their own apical domains for opening and closure in an ATP-controlled fashion. Here we use small-angle neutron scattering to analyze structural changes of the recombinant alpha-only and the native alphabeta-thermosome from Thermoplasma acidophilum upon their ATPase cycling in solution. We show that specific high-salt conditions, but not the presence of MgATP alone, induce formation of higher order thermosome aggregates. The mechanism of the open-closed transition of the thermosome is strongly temperature-dependent. ATP binding to the chaperonin appears to be a two-step process: at lower temperatures an open state of the ATP-thermosome is predominant, whereas heating to physiological temperatures induces its switching to a closed state. Our data reveal an analogy between the ATPase cycles of the two groups of chaperonins and enable us to put forward a model of thermosome action.
伴侣蛋白介导的蛋白质折叠由ATP结合和水解提供动力。ATP酶活性通过一系列构象重排驱动折叠机器，这在大肠杆菌的I型伴侣蛋白GroEL中已有广泛描述，但对II型伴侣蛋白仍知之甚少。后者——古菌热体和真核TRiC/CCT——独立于类似GroES的共伴侣蛋白发挥作用，并被认为依赖于其自身顶端结构域的突出部分以ATP控制的方式进行打开和关闭。在这里，我们使用小角中子散射来分析嗜热栖热袍菌重组的仅α亚基和天然αβ热体在溶液中进行ATP酶循环时的结构变化。我们表明，特定的高盐条件而非单独存在的MgATP会诱导形成更高阶的热体聚集体。热体开闭转变的机制强烈依赖于温度。ATP与伴侣蛋白的结合似乎是一个两步过程：在较低温度下，ATP-热体的开放状态占主导，而加热到生理温度会促使其转变为关闭状态。我们的数据揭示了两组伴侣蛋白ATP酶循环之间的相似性，并使我们能够提出一个热体作用模型。
